The overall aim of this project is to characterize a novel purinergic slow excitatory postsynaptic potential (EPSP) that is mediated by a metabotropic ATP receptor (P2Y1 receptor) in the enteric nervous system. Evidence for the existence of the purinergic slows EPSP emerged from pilot studies in which the P2Y1 receptor antagonist MRS2179 selectively blocked both the slow EPSP and slow EPSP-like responses evoked by ATP in submucosal neurons. The hypothesis that the purinergic slow EPSP is mediated by synaptic release of ATP and P2Y1 receptors in submucosal secretomotor neurons will be tested pharmacologically in morphologically identified neurons. Molecular cloning and functional expression will be used to better characterize the P2Y1 receptor. The proposal emerged from pilot/feasibility results, which suggest the hypothesis that intestinal secretomotor neurons receive purinergic slow excitatory synaptic input from neurons in the myenteric plexus, from neighboring neurons in the submucosal plexus and from sympathetic neurons in prevertebral ganglia. Added support for the hypothesis came from the discovery that the selective P2Y1 receptor antagonist MRS2179 suppressed neurogenic secretory responses evoked by application of ATP and by transmural electrical stimulation of secretomotor neurons in Ussing chamber experiments. Fulfilling the aims of this proposal will lead to better understanding of the role of a newly discovered purinergic slow EPSP in the enteric nervous system at the cellular, molecular and integrated system levels. The pilot/feasibility data are the first to demonstrate a functional purinergic slow EPSP in the enteric nervous system. The discovery that a P2Y1 receptor mediates the slow EPSP in intestinal secretomotor neurons might help in development of new drugs for treatment of the irritable bowel syndrome, inflammatory bowel disease and other disorders of defecation by targeting the P2Y1 receptor or ATP metabolic pathways in the pool of enteric neurons that control intestinal secretion. [unreadable] [unreadable]